In one type of micromachined device for measuring a rate of rotation about a rate axis, a planar mass is dithered, or oscillated, along a dither axis at a constant frequency. The dither axis is perpendicular to the rate axis, with the plane of the mass parallel to both the dither axis and the rate axis. This dithering causes the mass to experience a Coriolis acceleration along a sensitive axis, which is orthogonal to the plane of the mass (and to the dither axis and the rate axis), when the mass rotates about the rate axis. This Coriolis acceleration is proportional to the dithering velocity and to the angular rate of rotation, and therefore, has a frequency related to the frequency at which the mass is dithered.
A planar Coriolis electrode parallel to the plane of the mass senses a change in capacitance caused by an acceleration along the sensitive axis. The change in capacitance is used to measure the acceleration. In addition to the periodic rotational component (from the Coriolis acceleration) with a frequency related to the dithering frequency, the acceleration may have a DC component caused by a force acting linearly along the sensitive axis. To separate the rotational and linear components of the acceleration, two adjacent masses are separately dithered with identical sinusoidal signals with opposite phase. The resulting output signals from the two masses can be added or subtracted to cancel the rotational or linear components, respectively.
In another particular version of such a micromachined device, a micromachined rotor is suspended from a frame by four elastic beams that converge at a central anchor point. The rotor has four, small radial projections that have fingers that interdigitate with comb fingers to rotationally dither the rotor. This motion generates a periodic momentum vector along a sensitive axis that is perpendicular to a plane of rotation. The rotor can thus be used to detect rotation about an axis in the two dimensional plane of rotation. In this particular device, the Coriolis electrodes are small and the structure is not balanced, thus causing instability. Moreover, the device is subject to external influences, and therefore may provide less accurate measurement than desired.